It has been known to produce a resilient polyurethane foam and a polyurethane elastomer, by reacting a polyether polyol with an isocyanate group-containing low molecular weight compound in the presence of a foaming agent. An alkali catalyst such as potassium hydroxide has been known as a catalyst for producing said polyether polyol.
In a case of producing a polyether polyol by subjecting an alkylene oxide to a ring-opening polymerization reaction by using said alkali catalyst, a monol (unsaturated monol) having unsaturated groups will be formed as by-product, and the amount of the unsaturated monol will increase with the increase in the molecular weight of the polyether polyol (decrease in hydroxyl number X). Accordingly, with a polyether polyol having a hydroxyl number of 34, for example, the unsaturation is usually at a level of 0.08 meq/g.
In a case of producing a resilient polyurethane foam by using this polyether polyol having a relatively high unsaturation of a level of 0.08 meq/g, problems may arise such as decrease in hardness, decrease in ball rebound, deterioration in compression set, and decrease in curing property at the time of forming a foam.
Further, in a case of producing a polyurethane elastomer by using a polyether polyol having a relatively high unsaturation, problems may arise such as insufficiency in strength, decrease in elongation and failure in tack.
On the other hand, it has been known to use a double metal cyanide complex as a catalyst for ring-opening polymerization reaction of an alkylene oxide (U.S. Pat. Nos. 3,278,457-9). A method for producing a double metal cyanide complex is disclosed in e.g. U.S. Pat. No. 3,427,256, U.S. Pat. No. 3,941,849, U.S. Pat. No. 4,472,560 and U.S. Pat. No. 4,477,589, and a method for producing a polyether polyol by using a double metal cyanide complex as a catalyst is disclosed in e.g. U.S. Pat. No. 4,055,188 and U.S. Pat. No. 4,721,818.
Further, e.g. JP-A-3-14812 discloses that in a case where a resilient polyurethane foam is produced by using a polyether polyol produced by using a double metal cyanide complex as a catalyst and having, for example, a hydroxyl number of 34 and a low unsaturation of at most 0.02 meq/g, the above-mentioned problems such as decrease in hardness, decrease in ball rebound, deterioration in compression set, and decrease in curing property at the time of forming a foam, can significantly be overcome, and further, comfortableness to sit on will improve. However, it has been still desired to improve molding properties, particularly easiness in crushing.
Further, JP-A-4-145123 and JP-A-8-311171 disclose to use tert-butyl alcohol as a ligand for the double metal cyanide complex. In a case of producing a resilient polyurethane foam by using the polyether polyol produced by using said double metal cyanide complex as a catalyst, molding properties of the obtained foam are also inadequate, particularly in view of uneasiness in crushing. Further, the polyether polyol produced by using said double metal cyanide complex as a catalyst, has a spread molecular-weight distribution and a high viscosity and unfavorably influences physical properties of the obtained polyurethane elastomer if the molecular weight per hydroxyl group exceeds about 3000.
Further, U.S. Pat. No. 5,627,120 discloses to use tripropylene glycol monomethyl ether as a ligand for the double metal cyanide complex. In a case of producing a resilient polyurethane foam by using the polyether polyol produced by using said double metal cyanide complex as a catalyst, the molding properties of the obtained foam are also inadequate particularly in view of uneasiness in crushing.
In recent years, various studies have been made to improve performances of a resilient polyurethane foam. Particularly, along with enlargement of a sheet cushion, increase in the thickness of a product, and complication of the shape, it has been desired to improve performances called molding properties such as easiness in crushing, in addition to comfortableness to sit on. "Easiness in crushing" is referred to as "crushing property" and meant to be easiness in operation to crush the foam by e.g. a roller for connection of the foam released from the mold, i.e. crushing. If the closed cell ratio of the foam is high, cracks will form on the foam at the time of crushing, and such is unfavorable, and when the closed cell ratio is low, crushing can easily be carried out.
With respect to a resilient polyurethane foam produced by using a polyether polyol produced by using a double metal cyanide complex which has conventionally been proposed as a catalyst, performances of the foam are not adequate, and particularly crushing property of the sheet cushion is poor, such being problematic. Accordingly, in a case of forming a sheet cushion having a large size and a complicated shape, failure in forming will frequently arise, such being problematic. Further, physical properties of a polyurethane elastomer produced by using the polyether polyol produced by using said double metal cyanide complex catalyst is not adequate.